Corrosion protection of metals



.im so. 1945 CORROSION PROTECTION OF METALS Ellis Ross White, Albany, CaliL, assignor to.S hell Development Company, San Francisco, Calif.,

a corporation of Delaware 0 Drawing. Applicatlon'Februai-y a, 1945,

Serial No. 415.207

14 Claims. (oi. lie-cs) The present invention relates to metals or metal-containing articles of manufacture which are normally subject to corrosion and which have been rendered substantially non-corrodible by a treatment with a dispersion of certain mercapto monocarboxylic acids.

Metallic surfaces, particularly those containing iron, require protection against the hazard of corrosion in the presence of water. To illustrate: Moisture readily attacks finished or semi-finished metal objects unless the metal surface is covered during storage or shipment by a protective coatin; such as a slushing oil; water in Diesel engine fuels often corrodes closely fitted parts such as are found in Diesel engine unit type injectors;

.water in turbines corrodes turbine. lubricant cirterioration of various organic compounds with which they come in contact or may enter between moving parts of machinery where they act as abrasives.

It is a purpose of this invention to treat metals or articles or" manufacture containing metals in a way so that they become resistant to their normal corrosion. It is a specific purpose to treat in a simple manner accurately machined metal parts so that they may be handled without developlng corrosion, particularly in places where fingerprints have been left. Another purpose is to protect iron or steel equipment exposed to the atmosphere so that its rusting is prevented or at least retarded. Still another purpose is to protect mechanical equipment from rusting, which equipment stands idle and/or is shipped over long distances.

I have discovered that structural metals which are used in the-construction of various articles or manufacture and are subject to a normal corrosion can be protected simply and eflectively by treating them with a fine dispersion of an alpha i or beta mercapto monocarboxyllc acid containing at least 10 and preferably 12-30 carbon atoms.

The dispersion may be a true or colloidal solution in a suitable vehicle which'is capable of flowin: under the conditions of the treatment, 1. e..

' is liquid or plastic at the temperature or the treatment.

The treating temperature is preferably about atmospheric if the vehicle is normally liquid, although lower or higher temperatures maybe employed. The lower temperature limit is usually determined by the solidification temperature of the liquid, and temperatures should be below the boiling temperature of the vehicle and below the decomposition temperatures of both the vehicle and the dicarboxylic acid. f

Metals "capable of being thus protected are in particular the ferrous metals, e. g,, soft iron, various steels, cast iron, and to a lesser extent copper, brass, bronze,.zinc, aluminum, magnesium alloys, various bearing metals as copper-lead, cadmiumnickel, silver-nickel, etc.

Articles containing these metals are too numerolis to recite. However, it may be mentioned that the problem of rust prevention is critical, for example, where accurately machined parts are involved, such as piston rings, engine cylinders, bearing shafts, plungers of pumps, etc. In

other instances, rust prevention may perhaps not be critical, butof vast economic importance. as, for example, in the mass production of steel'castings which are piled up and often set in theopen for months before being finished.

Corrosion may be due not only to atmospheric exposure, but may be caused or accelerated by contact with acidic materials, for example, by touching with the fingers. It also may occur in closed systems, as in internal combustion engines, steam turbines, pipe lines, etc., due to the corrosive influence of various impurities as water,

oxygen, CO2, salts, inorganic or organic acids, etc.

The treatment, according to this invention, for the prevention of corrosion may consist of a singlecontact of the metal to be protected with the dispersion containing the dicarboxylic acid, or may comprise repeated contacts effected at intervals, or may consist of a continuous treatment lasting as long as the use of the particular dispersion or piece of equipment or both. The choice of any particular type of these treatments is usually dictated by circumstances. For example, if

' I newly machined and finished machine parts are to be rust-proofed, they may be clipped or sprayed with a suitable dispersion, and then stored away. On the other hand, if rust prevention in a steam turbine is desired, it is preferable that the circulating lubricating oil contain the active rust-preventive compound and contact is made as long as this oil is used. Should, after a while, this 011. be

discarded and be replaced by another one not containing a rust-preventive, then corrosion protection usually lasts for a long time thereafter, due

to the protective film left behind. In cases where this film .is mechanically destroyed, as in bearings, etc., running under extreme loads, the protective film must be renewed continuously; otherwiserustprotection fails.

Mercapto-carboxylic acids suitable for my purpose are hydrocarbon carboxylic acid hydrosulfides, wherein the hydrosulfide radical is in alpha or beta position to the carboxyl radical. If desired, the acids may contain inorganic substituents which are not too strongly polar, such as chlorine, ether, etc., radicals, but should preferably be free from highly polar substituents, such as hydroxyl, amino, nitro, carbonyl, or additional carboxyl and hydrosulfide radicals. For maximum stability against deterioration by oxidation, the acids should contain not more than one olefinic double bond, and pref eralbly none.

These mercapto-carboxylic acids can be produced quite readily by reacting a suitable halogenated hydrocarbon carboxylic acid with KSH or NaSH.

Examples of suitable hydrocarbon carboxylic acids are fatty acids, such as undecylic, lauric, myrlstic, palmitic, stearic, oleic, arachic, behenic, etc., acids; naphthenic acids such as maybe recovered from petroleum oils by extraction with caustic alkali; synthetic naphthenic acids, such as cyclohexyl-heptylic, -nonylic, -undecylic,

-lauric, -palmitic, -stearic, etc., acids, correspond;

ing methyl, cyclohexyl, ethyl cyclohexyl, dimethyl cyclohexyl, higher alkyl cyclohexyl, etc., fatty acids; fatty acids having two or more cyclohexyl radicals; aromatic fatty acids, such as phenyl-, tolyl-, xylyl-, benzal, naphthyl-, tetrallyl, etc., lauric; myristic, palmitic, stearic, arachic, etc.,

' acids.

The mechanism by which the mercapto-carboxylic acids assert their' corrosion-protective and extreme pressure properties is believed to be as follows:

The carboxylic acid radical being highly polar is attracted to the metal surface, where as a result of this attraction, a relatively high concentration of the acid exists and a protective film of the acid is formed. Because of the high concentration, two things happen: First, the sulfur becomes far more active than could normally be expected by taking-into consideration its concentration in suspension; and, second, a portion of the mercapto acid is oxidized to bis-carboxylic or basic, preferably having dissociation constants not above about 10-. In vehicles of low dielectric constant, as hydrocarbon oils, which are not conducive to ionization of dissolved electrolytes, relatively small amounts, i. e., about .1 %-5% of various carboxylic acids, such as fatty or naphthenic acids, may be present, and in many instances this 7 glycerol, methyl glycerol, etc.;' phenol and varimay even be beneficial Both polar and non-polar vehicles may be employed. Among the former are water, alcohols, such as methyl, ethyl, propyl, isopropyl,: butyl, amyl, hexyl, cyclohexyl, h'eptyl', methyl cyclohexyl, octyl, decyl, lauryl, myristyl, cetyl, stearyl, benzyl, etc., alcohols; polyhydric alcohols as ethylene glycol, propylene glycol, butylene glycol.

ous alkyl phenols; ketones as acetone, methyl ethyl ketone, 'diethyl ketone, methyl propyl, meththiophosphates, carbonates; natural waxes as acid disulfide, which is a very potent corrosion inhibitor.

. The vehicles to which the mercapto-carboxylic acids of this invention may be added for the purposeof producing corrosion-protective compositions may be divided into several groups. In the first place, they may be liquids or plastics, the only requirements as to their physical state being (in addition to their being able to act as carrier for the acids under normal atmospheric conditions) that they be spreadable over metal surfaces. Spreading may be accomplished by immersing, flooding, spraying, brushing, trowelling, etc.

After being applied, all or part of the vehicle may evaporate, or it may be more or less permanent. In other words, both volatile carriers may be used, or substances which do not materially volatilize-under normal atmospheric conditions. As to chemical requirements, the vehicle must be stable under ordinary conditions of storage and use and be inert to the active inhibitors.

Thus the vehicle should preferabl be substantially neutral, although it may be weakly acidic carnauba wax, candellila wax, Japan wax, jojoba" oil, sperm oil; fats as tallow, lard oil, olive oil, cottonseed oil, perilla oil, linseed oil, tung oil, soya-bean oil, flaxseed oil, etc; weak bases as pyridine, alkyl pyridines, quinolines, petroleum bases, etc.

Vehicles of little or no polarity comprise hydrocarbons or halogenated hydrocarbons as liquid butanes, pentanes, hexanes, heptanes, octanes, benzene, toluene, xylenes, cumene, indene, hydrindene, alkyl naphthalenes; gasoline distillates, kerosene, gas oil, lubricating oils (which may be soap-thickened to form greases), petrolatum, parafiin wax, albino asphalt, carbon tetrachloride, ethylene dichloride, propyl chloride, butylchloride, -chlor benzol, chlorinated kerosene, chlorinated paraffin wax, etc.

The amounts of the mercapto-carboxylic acids which must be incorporated in the above vehicles to produce corrosion-protective compositions vary considerably with the type of vehicle used. As

' amounts required of the mercapto-carboxylic acids vary from about .00l% up to about .l%, although larger amounts, say 1.0%, may be used,

However, where the acids are in colloidal dispersion, rather than in true solution, a concentration in excess of about .1% may result in relatively asoaeov large amounts of colloidally dispersed inhibitors, together with resin, may be quite resistant to precipitation and settling.

Since resinous and gummy substances in the vehicles do call for greater amounts of inhibitors, it is usually desirable to refine normally liquid vehicles thoroughly'and free them from gummy substances, thereby imparting to them maximum inhibitor susceptibility. This is of particular importance'ffor example, in lubricating oils, specifically steam turbine oils, which are advantageously highly refined before the inhibitor is introduced. Suitable refining treatments include.

for example, extraction with selective solvent for aromatic hydrocarbons as liquid 80:, phenol, furfural, nitrobenzene, aniline, beta-beta-dichlorine diethyl ether. antimony trichloride, etc.; treatment with AlCla, sulfuric acid, clay. etc.; as. the treatment produces a sludge, special care must a be taken to remove it very thoroughly and com-- pletely.

Example I The effectiveness of alpha mercapto stearic acid in suppressing corrosion was determined by a test wherein a polished steel strip was subjected to the action of a vigorously stirred emulsion of a turbo rafilnate oil having S. U. viscosity at 100 F. of 150 seconds, with 10% by volume of water at 167 F. When using distilled water, .01% of the acid in the oil gave perfect protection. In

synthetic sea water spots appeared in 24 hours,

and in 48 hours about 5% was corroded.

Example I! The extreme pressure property of alpha mercapto lauric acid was tested by making solutions of difierent concentrations of this acid in a 55 V. I. light motor oil having a Bay. Univ. viscosity of 155 at 100 F., and running them in the fourball machine described in Engineering," vol. 136 (1933), page 46, for 2 hours at 7 kg. load at-130 C. The scar diameters on the top balls were then measured and found to be as follows:

Percent alpha mercapto laurie acid streets.

I claim as my invention: 1. A structural normally corrodible metal coated with a corrosion-preventive film of a hydrocarbon monocarboxylic acid hydrosulfide selected from the group consisting of the alpha and beta hydrosulfide acids having from 10-30 carbon atoms. 2. A structural normally corrodible metal Scardiamcorridible metal corrodible metal spreading over its surface a fine dispersion in a beta hydrosulfide acids having from 1040 carbon atoms, the hydrocarbon radical of said acid containing chlorine. v

3. A structural normally corrodible metal coated with a corrosion-preventive fihn 01' a hydrocarbon monocarboxylic acid alpha hydrosulfide having from 10-30 carbon atoms.

4. A structural normally corrodible met coated with a corrosion-preventive film of a hydrocarbon monocarboxylic acid beta hydrosulfide having from 10-30 carbon atoms.

5. A structural normally corrodible metal coated with a corrosion-preventive film of an alpha mercapto stearic acid.

6. A structural normally corrodible metal coated with a corrosion-preventive film of a mercapto naphthenic acid selected from the group consisting of alpha and beta mercapto acids having from 10-30 carbon atoms.

7. A structural normally corrodible metal coated with a corrosion preventive film of a mercapto aromatic fatty acid selected from the group consisting of alpha and beta mercapto acids having from 10-30 carbon atoms.

8. A ferrous metal coated with a rust-preventive film of a hydrocarbon monocarboxylic acid hydrosulfide selected from the group consisting of the alpha and beta hydrosulfide acids havins at least 10-30 carbon atoms.

9. An article of manufacture comprising a structural normally corrodible metal treated with a fine dispersion in a substantially neutral vehicle of a hydrocarbon monoc'arboxylic acid hydrosulfide selected from the group consisting of the alpha and beta hydrosulfide acids having from 10-30 carbon atoms.

10. Method of protecting a structural normally corrodible metal from corrosion comprising spreading over its surface a fine dispersion in a substantially neutral vehicle of a hydrocarbon monocarboxylic acid hydrosulfide selected from the group consisting of the alpha and beta hydrosulfide acids having from 10-30 carbon atoms.

11. Method of protecting structural normally from corrosion comprising spreading over its surface a fine dispersion in a substantially neutral vehicleof an alpha mercapto fatty acid having from 10-30 carbon atoms.

12. Method of protecting structural normally corrodible metal from corrosion comprising spreading over its surface a fine dispersion in a substantially neutral vehicle of an alpha mercapto stearic acid. v

13. Method of protecting structural normally from corrosion comprising substantially neutral vehicle of an alpha mercapto naphthenic acid having from 10-80 carbon atoms.

14. Method of protecting structural normally corrodible metal from corrosion comprising spreading over its surface a fine dispersion in a substantially neutral vehicle of analpha mercapto aromatic fatty acid having from 10-30 carbonatoms. 

